Under certain conditions which are generally known, there is a formation of solid ferric oxide (Fe.sub.2 O.sub.3) and or formation of ferrosoferric oxide (Fe.sub.2 O.sub.3.FeO) which forms on some iron containing materials in contact with water. These iron oxides can be especially troublesome when water flow passages are diverted or blocked partially or more. One example of this type of blockage and the problem that this blockage creates would be a steel, or coated steel storage tank connected via iron or copper pipe to a copper coil, and/or coil and heat exchanger, or heat exchange only hot water heater. Normally, this system contains a circulating pump which causes a velocity flow between the storage tank and the water heater of the described type. The turbulence caused by this water flow can agitate or break loose iron oxide chunks from a corroded steel source, which may be carried into the passages of the copper coil type water heater and lodge therein causing a blockage preventing the proper flow of water through the water heater. This condition can bring about extreme heat rise, steam flashes, copper heat stress and failure, and possibly an explosion. Many times the entire blocked coil and or heat exchanger must be replaced since there is currently no recognized chemical method to remove the iron oxide, which does not simultaneously destroy the copper tubing and/or result in the evolution of noxious gases.
Where possible, physical methods of iron oxide removal are attempted, though often this is impractical. Methods to remove these chunks have included where possible, tear down of a heat exchanger where the water heater design includes header plates, the trial of high pressure back flushing, and/or the nearly impractical removal of U-bends where 16 or more might have to be unbrazed and then rebrazed. These very expensive and time consuming methods are the best available up to this time and the complete replacement of the coil or heat exchanger is often necessary.
Slight chemical action has been reported with very small amounts in the microgram or low milligram range of iron oxides tested. Some of these results have been the basis for products which are sold as rust removers, or rust stain removers. Very little activity against solid iron oxide of the type described in this invention occurs when these chemicals are tested.
Moreover, in a commercial environment, days or months are far too long for a chemical reaction to occur. Reasonably, a hot water heater should be repaired in a matter of hours, not days. Alkaline solutions of such chelating and sequestering agents as sodium glucoheptonate, sodium gluconate, sodium polyphosphates seqlene 270, seqlene ES-50, acidic solutions of ethylenediaminetetraacetic acid (EDTA) showed no reaction or weight loss to the iron oxide samples after contact time exceeding 336 hours. It is reported that an effective method of dissolving iron oxide is to place it in near boiling concentrated hydrochloric acid. Nitric and sulfuric acids are claimed to have very little or no effect on solid iron oxide. Concentrated near boiling hydrochloric acid cannot be used in a copper system since it also dissolves copper. The extreme toxicity, corrosive, and poisonous nature coupled with the difficulty of available safe engineering controls, precludes the use of this material in a routine manner.